We identified a unique marker of invading glioma cells that arises from PTP cleavage. We developed a specific molecular imaging probe that binds to the cleaved PTP fragment and recognizes glioblastomas. Therefore, we will test the hypothesis that this probe marks high-grade human gliomas and defines the invading tumor margin. We will explore its utility as a diagnostic molecular imaging agent and as a therapeutic. Primary brain tumors commonly arise from supporting glial cells within the central nervous system. These tumors are called gliomas and typically disperse widely throughout the brain making complete surgical resection impossible. The invasive properties of gliomas lead to difficulties in determining the extent of invasion and make this disease virtually incurable with a mean survival of approximately one year. PTP is a cell surface receptor protein tyrosine phosphatase (RPTP) and a cell adhesion molecule whose expression is down-regulated in human gliomas. Very recent data suggests that during PTP down-regulation, the protein is proteolyzed and a small fragment remains associated with the glioblastoma cells. Here we describe studies that utilize a unique robust molecular imaging probe for the PTP fragment and test its effectiveness in vivo. Our hypothesis is that the probe will detect the migrating and invading glioblastomas at the cellular level and can eventually be used in human patients to image the tumors with magnetic resonance imaging (MRI). Identification of key molecular targets such as PTP will allow development of novel strategies to diagnose, image and eventually treat gliomas. It is envisioned that this probe could also be utilized during surgery to guide neurosurgery of the tumors enabling more complete and precise tumor resection, which will enhance patient survival. Aim 1: Determine the extent of association of the cleaved fragment of PTP with invasiveness of human gliomas of various types and grades. Aim 2: Assess the utility of peptide probes to monitor migrating glioma cells in an ex vivo brain slice invasion assay. Aim 3: Examine the utility of the probe to detect tumors and migrating glioma cells in vivo in heterotopic and orthotopic human brain tumor models in rodents.